The leading source of carbon emissions in the United States is oil combustion and by quite a bit. In fact, burning oil accounts for about 30% more carbon emissions than the next leading source which is coal.
Yet, carbon emissions from coal, natural gas, and oil headed in different directions in the first 2 months of 2013. Emissions from oil are down again and significantly, but emissions from oil and gas are up. What does that rising and falling add up to?
US carbon emissions in the first two months of 2013 are up 1.5% compared to the same period in 2012.
http://www.eia.gov/totalenergy/data/monthly/pdf/mer.pdf. See Section 12 of the May Report.
While emissions from coal and gas rose in January and February, emissions from oil declined 2%. Despite the falling emissions from oil, the increases in emissions from coal and gas were substantial enough to raise total emissions.
Why did emissions from coal and natural gas increase in the first two months? More coal was used to generate power and more gas was used to heat buildings, as this year's winter was a bit colder than the record warm temperatures of 2012.
Emissions from oil fell, as a result of greater fuel efficiency in vehicles and continuing movement to oil substitutes like electricity, gas, and biofuels. The continuing decline in emissions from oil--the leading source of US carbon emissions--is a bright spot in the 2013 carbon data that probably will see a rise in total carbon emissions primarily as a result of a significant increase in the use of coal to make electricity.